Formulations curable with visible or ultraviolet light are known from various technological fields, such as coating, printing and electronics. The use of such compositions in molding techniques is also known. In the “shape deposition manufacturing” method (U.S. Pat. No. 6,342,541), for example, casting molds for complex molded parts are produced by means of UV-curable formulations by curing, on a base plate made of wax, a layer of the liquid formulation by means of ultraviolet light, machining this layer and then surrounding it with new wax. This procedure is repeated until the desired wax mold, filled with the cured composition serving as support material, is obtained. Subsequently, the support material is dissolved out by means of an aqueous alkali lye, so that the empty wax mold can be used for further molding processes.
The U.S. Pat. No. 6,375,880 describes similar support materials for a molding method wherein the support material is removed either by dissolving or by melting; however, it does not give any information on the chemical composition of these materials.
A disadvantage of both molding techniques is the requirement of mechanical machining each individual layer after curing, which makes the production of complex molded parts with undercuts difficult or impossible. Furthermore, planning processes for CNC (“computer numerical control”) production is rather complicated.
In stereolithography, this is avoided by selective curing (J.-C. André, A. Le Méhaute, and O. De Witt, FR-A-2,567,668 (1986), A. J. Herbert, J. Appl. Photo. Eng. 8(4), 185-188 (1982), C. Hull., U.S. Pat. No. 4,575,330 (1986)). On a building platform, thin resin layers are selectively cured in succession in a resin bath (e.g. by scanning with a UV laser or selective exposure), so that molded parts are obtained without mechanical working steps. Resin formulations based on acrylate or epoxy resins that have been used in such procedures so far, such as those described in the WO 01/12679, result in crosslinked and thus insoluble and non-meltable components, which are as such used as end products, for example as plastic inserts in dental technology.
This involves the disadvantage that the properties of such a component are determined by the composition of the liquid formulation used, which is only variable to a limited extent due to the requirement of being curable with light. The production of molded parts made of other materials requires further steps in which the insoluble and non-meltable component serves as original mold for producing casting molds. In silicone molding, for example, the original mold is embedded in silicone and then mechanically removed from the soft silicone mold thus obtained. Apart from the additional amount of work involved, mechanical removal is only possible with parts without or with only few undercuts, which makes this method unsuitable for the production of complex components.
Another possibility is insert molding, wherein a casting mold of inorganic material is produced by aid of the original mold, followed by removing the original mold by thermal decomposition. This requires not only a considerable amount of energy, but also casting mold materials tolerating temperatures of up to approximately 600° C.
Alternatively, AT-A-412,399 describes photopolymerizable water-soluble compositions that may be cured selectively and result in water-soluble polymers. This permits the production of complex components, even with deep undercuts, without mechanical treatment of the casting molds.
However, these water-soluble materials have a limited range of use. For example, aqueous processing aids cannot be used in such a molding process as they lead to swelling and solubilization of the original mold. Furthermore, swelling of the material may even be caused by air humidity, leading to reduced dimensional accuracy and thus to a deterioration of the exact geometry of molded parts.
Consequently, a number of important materials processed from aqueous formulations are not suitable for this process, e.g. materials from the field of sol-gel chemistry or gel casting. Especially gel casting permits the production of far more complex geometries than conventional methods of ceramic molding. Here, water-soluble molding materials are not suitable since such ceramic components are produced from water-based gels (see F. Costa et al., Journal of Non-Crystalline Solids 345-46, 787-789 (2004), V. K. Parashar et al., Microelectronic Engineering 67-8, 710-719 (2003), Y. F. Gu et al., Ceramics International 25 (8), 705-709 (1999)).
Molding biomaterials for medical applications, e.g. hydrogel materials with complex conduits and networks, or producing framework structures based on biocompatible and biodegradable composites (e.g. aliphatic polyesters based on glycolic acids or lactones; see S. Limpanuphap et al., Journal of Materials Science-Materials in Medicine 13(12), 1163-1166 (2002)) is not possible with such water-soluble compositions.
A further disadvantage of water-soluble compositions is the generally low dissolution rate of polymers in water, which often results in delays in the production process of molded parts.
Thus, one object of the invention is to overcome the above disadvantages by improving molding procedures and/or the curable compositions used therein, such as radiation-curable formulations, which may be selectively cured and processed to mechanically stable casting molds for complex components without mechanical treatment. These casting molds should not swell due to existing air humidity and thus permit improved molding accuracy as well as the use of materials processed from aqueous systems. Further objects of the invention are to provide high dissolution rates for the molds in appropriate solvents and quick melting of the molds as well as improved mechanical properties of the molding materials, which results in advantages during production.